1. Field of the Invention
The present invention relates to an on-off valve provided between an evacuation apparatus and a process chamber in which a semiconductor wafer or the like is processed under reduced pressure, and to a process apparatus employing the on-off valve.
2. Description of the Related Art
When semiconductor devices are fabricated, various vacuum processes including a thin film deposition process, an etching process, and the like are carried out in process apparatuses having a chamber that can be evacuated to reduced pressure. A semiconductor wafer, which is subjected to the process, is transferred into the chamber, and undergoes predetermined processes while the chamber is evacuated by an evacuation apparatus such as a vacuum pump connected to the chamber via a vacuum line.
During the process in the chamber, the chamber pressure is controlled by adjusting the degree of opening a pressure control valve located in the vacuum line between the chamber and the vacuum pump.
In addition to the pressure control valve, an on-off valve is provided upstream or downstream of the vacuum pump in the vacuum line, in order to prevent the interior of the vacuum line from being unduly exposed to the atmosphere when the process apparatus and/or the vacuum apparatus is down for maintenance.
An example of such an on-off valve is disclosed in Patent Document 1 (Japanese Patent Application Laid-Open Publication No. H09-89139). As described in the publication, a conventional on-off valve is closed when a closure element comes in tight contact with a valve seat having an opening in order to close the opening, and opened when the closure element comes off the valve seat in order to allow a gas flow path through the opening. In order to ensure a tight closure of the valve, a ring-shaped seal member made of an elastic material is attached on the closure element. The seal member is elastically deformed when the closure element is pressed onto the valve seal in order to fully eliminate a gap between the closure element (the sealing member) and the valve seat.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. H09-89139
In the above conventional on-off valve, since the closure element is linearly movable, the closure element is positioned away from the valve seat in order to face the opening of the valve seat when the valve is open. Therefore, the seal member attached on the closure element of the on-off valve is exposed to gases including CF gas and O2 gas, which are used as a process gas or a cleaning gas in the process chamber of the process apparatus employing the on-off valve, when the on-off valve is open. Due to the exposure to the gases or to active species (radicals, ions) activated by plasma in the process chamber, the seal member may become deteriorated, so that sealing performance is impaired and particles may be caused to break off. As a result, the process apparatus has to be frequently down for maintenance in order to replace the seal members of the on-off valve.
In order to reduce the frequency of seal member replacements, a seal member made of a fluorinated rubber, which has high resistance to plasma and/or active species, is being used in response to a recent trend of high energy plasma being used in plasma processes. However, even such a seal member is not free from deterioration, which requires replacement of the seal member, for example, every several months. In addition, the seal member made of the fluorinated rubber is very expensive, which may increase maintenance costs. Moreover, since the process apparatus has to be down for maintenance when the seal members are being replaced, total fabrication throughput is impaired.